1. Field of the Invention
The present invention relates to a process cartridge and an image forming apparatus with it containing such a cartridge. The image forming apparatus may be, for example, a laser beam printer, an electrophotographic copying machine, a facsimile machine, a word processor or the like.
2. Related Background Art
In image forming apparatuses such as printers, a latent image is formed by selectively exposing a photosensitive drum (an image bearing member) which has been uniformly charged, and the latent image is then visualized with toner as a toner image which is in turn transferred onto a recording sheet, thereby recording an image on the recording sheet. In such apparatuses, whenever the toner is consumed or used up, new toner must be replenished. However, the toner replenishing operation not only is troublesome, but also often causes contamination of surrounding components. Further, maintenance of various elements must be performed periodically.
To this end, a so-called process cartridge wherein a photosensitive drum, a charger, a developing device, a cleaning device and the like are integrally contained in a cartridge housing which can be removably mounted to an image forming apparatus, whereby the replenishment of toner or the exchange of parts whose service lives have expired can be permitted and maintenance can be facilitated, has been proposed and put into practical use (for example, as disclosed in U.S. Pat. Nos. 3,985,436, 4,500,195, 4,540,268 and 4,627,701).
Since such a process cartridge is mounted to and dismounted from the image forming apparatus, it is necessary to detect and ascertain whether the process cartridge is positioned in the image forming apparatus before an image forming operation is started. In the past, the detection of the presence/absence of the cartridge has been mechanically effected by using a contact switch, an actuator and the like. That is to say, when the process cartridge is mounted to the image forming apparatus, the contact switch is turned ON by the actuator; whereas, when the cartridge is dismounted, the contact switch is turned OFF by the actuator. A signal from the contact switch is sent to a controller, thereby judging whether the cartridge is mounted to the image forming apparatus.
However, in the above-mentioned construction for detecting the presence of the process cartridge, since the mechanical parts such as the contact switch and actuator are used, the apparatus was made expensive.
Further, since the parts such as the contact switch and actuator must be provided, it was difficult to make the apparatus small-sized.
Furthermore, it has been desired that the presence/absence of developer in the process cartridge can be detected with a low cost and without making the image forming apparatus large-sized.